Eq. (REF ) gives a way to reduce the propagator of
two linear dependent vectors to just one. Together with the two-point splitting
lemma (REF ) we will geometrically construct the formula for
the reduction of three propagators with linear dependent vectors to the sum of two propagators.
The derived formula will be at the heart of the partial fraction decomposition for the NNLO real
correction of the Drell-Yan angular distribution (which we plan to investigate in the near future in the context of small \(Q_T\)  resummation, compare Ref. [1]} and [2]}).
